The present disclosure is directed to a fourth generation mobile communication system supporting ultra-high speed multimedia service evolved from the third generation system characterized by IMT-2000 high speed multimedia service that has been evolved from the first generation analog and second generation digital mobile communication systems in series.
One of the representative second generation mobile communication systems is CDMA 1x system. FIGS. 4 and 5 are graphs illustrating voice activity state variations during human speech. FIG. 4 shows the voice activity variation during the presence of speech, and FIG. 5 shows the voice activity variation during the absence of speech. In FIGS. 4 and 5, the y axis denotes voice activity state, and the voice activity states of CDMA 1x are categorized into full rate, half rate, 1/4 rate, and 1/8 rate. These voice activity states correspond to voice transfer rates of 9.6 kbps, 4.8 kbps, 2.7 kbps, and 1.5 kbps, respectively for transmitting voice data at different transmission power levels. The voice data is transmitted at 3.75 dB for 9.6 kbps transfer rate, −0.25 dB for 4.8 kbps transfer rate, −2.72 dB for 2.7 kbps transfer rate, and −5.875 dB for 1.5 kbps, compared to the uplink pilot channel. As previously mentioned, the transmission power of the uplink voice channel varies quite significantly according to the voice transfer rate in CDMA 1x system. If the voice transfer rate changes from the full rate to 1/8 rate, the transmission power decreases over 9-fold (9.625 dB). Such a significant change of voice transfer rate takes place frequently during the voice call session, especially in the speech section (see FIG. 4) rather than in the non-speech section (see FIG. 5). In FIG. 4, the abrupt change of voice transfer rate in the speech section is marked with circles. The change of voice transfer rate in the non-speech section takes place less abruptly and less frequently as shown in FIG. 5.
Among the third generation mobile communication systems, CDMA HRPD (High Rate Packet Data) and WCDMA HSPA (High Speed Packet Data) systems are representative examples of mobile communication systems having the channel structure for high speed data transmission. The CDMA HRPD system is a system based on Code Division Multiple Access (CDMA), and the typical structure of HRPD system includes a Packet Data Service Node (PDSN) 101 connected to the Internet and transmitting high speed packet data to a base station 103 and a Packet Control Function (PCF) 102 for controlling the base station 103, as shown in FIG. 1. The base station 103 performs radio communication with a plurality of mobile stations 104 and transmits high speed packet data to the mobile station having the highest data rate.
The fourth generation mobile communication system evolved from the third generation mobile communication system, such as a HRPD system, aims at a data rate of 20 Mbps or higher for ultra high-speed multimedia service and adopts an orthogonal frequency transmission scheme such as Orthogonal Frequency Division Multiplexing (OFDM). The Long Term Evolution (LTE) and LTE-Advanced (LTE-A) of the 3GPP standard are representative fourth generation mobile communication systems. Referring to FIG. 2, the LTE system includes evolved Node B (eNB) 202 performing radio communications with a plurality of User Equipment (UEs) 201 to provide high speed multimedia service, Mobility Management Entity/Serving Gateway (MME/S-GW) 203 for managing UE mobility, call processing, and data transfer path, and Packet Data Network Gateway (P-GW) 204 connected to the Internet to deliver the high speed packet data to the UE via the eNB.
In a system where the reverse (or downlink) resource is allocated to the UEs based on the eNB scheduling, the eNB should know the information regarding the power headroom of each UE for efficient scheduling. If the eNB has no information regarding the power headroom of the UE, the UE may be allocated a resource larger than the data amount to be transmitted in unit time duration based on the current power headroom, resulting in unnecessary waste of reverse (or uplink) resources. The LTE standard also specifies the power headroom report procedure. In LTE, the power headroom report is triggered when the downlink path-loss measured by the UE is greater than a predetermined threshold value.
However, the conventional power headroom report has a drawback in that the UE reports power headroom too many times in a short duration when the UE is moving at high speed or the radio channel of the UE varies frequently due to the ambient environment.